This invention relates to tenter frame clips used for clamping a web of material being transported on a tenter frame.
It is known to use tenter frames to stretch webs of materials, e.g., plastic films, fabrics, foils, etc., in the direction of their width. A typical tenter frame is described in Jungpeter et al., U.S. Pat. No. 4,065,838, and generally includes a plurality of tenter frame clips mounted on two endless chains guided by a pair of diverging tracks. The clips are adapted to shift from an open position to a closed position to grip the edges of a web of material such as plastic film. As the web is moved in the machine direction being gripped by the clips which are moving on the diverging tracks, the web can be stretched transversely simultaneous with its longitudinal movement.
In the operation of a tenter frame, means are provided to move the clamping arm of each clip to an open position to receive the edge of the web as it is moved into the location where the web is to be gripped. Means are there provided to shift each clamping arm to the closed position as the clips follow their divergent tracks. Finally, means are provided to shift each clamping arm open again to release the web as each clip follows its path around the endless chain. Such opening and closing means are well known to those skilled in the art. See, for example, Jungpeter et al., U.S. Pat. No. 4,085,838.
Thus, it can be seen that in the typical operation of a tenter frame there is a constantly repeated opening and closing of a great number of tenter frame clips as a continuous web is moved through the frame. The noise generated in the operation of a tenter frame can be at such a high level as to have adverse effects on the personnel in the area when they are exposed for a protracted period of time. This noise problem with its attendant wear and tear on the clip parts was referred to in Lane, U.S. Pat. No. 2,096,283, issued in 1937. Lane's solution was to reduce the number of openings and closings per circuit from four to two and thus cut the problem in half.
In the typical operation of a tenter frame clip in the stretching of plastic film, the primary source of the noise and wear in the operation is in the metal-to-metal contact between the clamping arm and the clip body when the clip is opened.